1. Field of the Invention
The present invention relates to table saws for cutting a workpiece by means of a cutting unit having, for example, a circular grinder or a rotary blade such as a saw blade. In particular, present invention relates to table saws that have a positioning fence for positioning and fixing a workpiece on a table and cut or perform other working operations on a workpiece by moving the cutting unit in a downward direction.
2. Description of the Related Art
Table saws have included a table for placing and fixing a workpiece thereon, and a cutting unit supported operably movable relative to the table in a vertical direction. The cutting unit has an electric motor as a power source and a circular rotary blade driven by the electric motor. When an operator moves the cutting unit vertically downward with the rotating rotary blade while the workpiece is fixed on the table, the rotary blade can cut into the workpiece to perform the cutting operation. A positioning fence is provided on the table for positioning a workpiece on a table surface direction (relative to a table surface). In the case of a cutting device having a turntable rotatably supported on a base, both end portions of the positioning fence are fixed to the base and the positioning fence extends over the turntable. Therefore, if the turntable type cutting device is used, the rotary blade can be moved from a perpendicular position to a tilted position relative to a positioning surface of the positioning fence when the table is rotated by a predetermined angle and the cutting unit is integrally rotated in a left or right direction. By this means, so-called oblique cutting operation can be performed. Further, besides the angle cutting operation, so-called inclined cutting operation can be performed, if the cutting unit is tilted in a direction, in which a rotational axis of the rotary blade is inclined relative to the upper surface of the table.
A positioning surface of the positioning fence contacts with a workpiece and a rotational axis of the table is positioned within a plane of the positioning surface.
This type of positioning fence is disclosed in U.S. Pat. No. 6,899,005, U.S. Pat. No. 5,755,148, Japanese Laid-Open Utility Model Publication No. 6-5820 and Japanese Patent No. 3286725. For example, movable positioning fences disclosed in U.S. Pat. No. 6,899,005 can slide in left and right directions relative to a rotary blade and have positioning surfaces that are positioned on the left and right sides of the rotary blade, respectively. According to this movable positioning fences, the above-mentioned oblique cutting operation or inclined cutting operation can be performed without interfering with the rotary blade by sliding one of movable fences in a direction away from the rotary blade. Conversely, if any one of the movable fences is slidably moved toward the rotary blade to form a high positioning surface, a relatively tall workpiece can be positioned standing diagonally between the upper surface of the table and the movable fence in an increased-height position.
The positioning surface of each of the positioning fences extends vertically upward above the table surface and is divided into an upper and a lower positioning surface. The upper positioning surface is defined by an upper movable fence member, which is slidably movable in left and right directions, however, the lower positioning surface is defined by a lower fence member fixed without being allowed to move. Therefore, the lower positioning surface must be fixed having a predetermined clearance to the rotary blade in order to perform the oblique cutting operation or inclined cutting operation.
Because the lower fence member must be fixed to have a sufficient clearance relative to the rotary blade, a narrow part of the workpiece is not allowed to contact with the positioning surface due to the clearance, for example, when the workpiece is vertically cut from the end with a small width (slicing operation). Therefore, it may be difficult to perform an exact cutting operation because a positioning accuracy for a narrow part of the workpiece is not ensured.
Thus there is a need in the art to provide a table saw that can securely avoid an interference with the rotary blade when an inclined cutting operation or an oblique cutting operation is performed. Further, there is a need to achieve a highly accurate positioning function even if the cutting operation is performed with a small width.